Add RmsProp optimizer.
Add RmsProp optimizer.

trungda/mlpack,ajjl/mlpack,ersanliqiao/mlpack,BookChan/mlpack,stereomatchingkiss/mlpack,chenmoshushi/mlpack,BookChan/mlpack,palashahuja/mlpack,thirdwing/mlpack,chenmoshushi/mlpack,stereomatchingkiss/mlpack,theranger/mlpack,ersanliqiao/mlpack,darcyliu/mlpack,trungda/mlpack,erubboli/mlpack,lezorich/mlpack,palashahuja/mlpack,trungda/mlpack,erubboli/mlpack,theranger/mlpack,datachand/mlpack,minhpqn/mlpack,theranger/mlpack,ranjan1990/mlpack,chenmoshushi/mlpack,erubboli/mlpack,darcyliu/mlpack,bmswgnp/mlpack,stereomatchingkiss/mlpack,ranjan1990/mlpack,lezorich/mlpack,darcyliu/mlpack,minhpqn/mlpack,bmswgnp/mlpack,ersanliqiao/mlpack,minhpqn/mlpack,ranjan1990/mlpack,datachand/mlpack,BookChan/mlpack,palashahuja/mlpack,thirdwing/mlpack,Azizou/mlpack,datachand/mlpack,ajjl/mlpack,Azizou/mlpack,bmswgnp/mlpack,ajjl/mlpack,lezorich/mlpack,thirdwing/mlpack,Azizou/mlpack